Glad you like it 
It works like this: when the particle falls, it eventually comes within the keep apart radius of a ‘pile’ particle, or hits the ground. If it hiths the ground, it becomes a ‘pile’ particle. If it comes within the keep apart radius, the KA applies a force to it, which slows its fall. When its speed falls below a threshold, it also becomes a ‘pile’ particle. Works great 

